With the rapid progress of nano scientific technology, an inorganic nanostructure such as a one-dimensional metal nanowire structure, etc. has received much attention because it is applicable to the fields such as an optical device, an optical waveguide, a biosensor, a magnetic storage medium, etc. In general, this nanowire is known to be directly synthesized by a vapor-liquid-solid (VLS) growth method. Growth rate of the synthesized nanowire can be estimated according to the kind of the catalyst material and the size of catalyst droplet used in this method. However, the VLS method has limitations in the scale (length, width, etc.), properties, or composition of the synthesizable nanowire, and has a disadvantage that it is difficult to grow a nanowire in the exact position. Accordingly, there is a continuous demand for a method of obtaining a nanowire by easily controlling the scale, properties, or composition of the nanowire.
Meanwhile, formation of a nanostructure through self-assembly of a block copolymer is a simple process and thus requires a low production cost. The chemical structure of the material is similar to the photoresist currently used, and thus there is an advantage that it can be easily applied to a semiconductor manufacturing process. The block copolymer includes polymer blocks having different chemical structures, connected through a covalent bond, and according to the compositions of blocks constituting the block copolymer, the length of the chain, and Flory-Huggins interaction parameter, it may form various nanostructures including a complicated three-dimensional structure such as a gyroid, or a HPL (hexagonal perforated lamellae) structure, as well as a basic structure such as a sphere, a cylinder, or a lamellae. Also, the size of the nanostructure may be controlled from 5 to 50 nm, according to chemical structure of the block copolymer, compositional ratio of blocks, the molecular weight thereof, etc. It has attracted much attention as a next-generation technology of forming nanostructures, because of applicability of a non-destructive process, simple production of a template for high density arrangement of nanostructures, etc.
Accordingly, recent basic studies have been actively conducted to form a variety of metal nanowires, nanomeshes, nanorings, etc. using the nanostructure of the block copolymer as a template or a reactive group. For example, Buriak's group has proposed that a cylindrical nanostructure of a polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer is regularly arranged in a topographic pattern having a width of several hundred nanometers or more, and then used for forming a metal nanowire. In this method, the P2VP blocks present inside the cylindrical structure thus arranged are allowed to be positively charged by acid treatment, and then negatively charged metal chloride ions are adsorbed onto the inside surface of the cylindrical structure by electrostatic attraction, and then only the block copolymers are selectively removed by plasma treatment so as to selectively form a regularly arranged metal nanowire on the surface of silicon substrate [Nature Nanotechnology 2007, 2, 464; Acs Nano 2008, 2, 489]. Meanwhile, Ross' group has manufactured a variety of metal (Ti, W, Pt, Co, Ni, Ta, Au, Al) nanowires by forming a horizontally arranged poly(styrene-b-dimethylsiloxane) (PS-b-PDMS) cylinder by solvent annealing and then conducting reactive ion etching using the same as a template [Nano Lett. 2010, 10, 3722].
Further, a method for forming a variety of metal nanomeshes by conducting a reverse pattern transfer process using a spherical nanostructure formed from the PS-b-PDMS block copolymer as a template was also proposed [Small 2009, 5, 1654]. In addition, Russell's group has manufactured a metal nanoring, etc. by forming an oriented poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) thin film vertical to a substrate by solvent annealing, forming a porous nanostructure by surface reconstruction, and then depositing gold onto the nano-scale porous nanostructure, followed by heat treatment [Nano Lett. 2008, 6, 1667].
However, in the above described conventional methods for forming a nanowire or nanomesh from a block copolymer, an acid aqueous solution was mainly used for adsorption of the metal precursor onto the block copolymer. For this reason, the kind of the adsorbable metal precursors and the kind of the applicable metals are restricted, for example, formation of silver (Ag) nanowires or nanomeshes was impossible. Moreover, an additional chemical or physical process such as surface treatment, middle layer coating, metal deposition, etc. is needed before the adsorption process of the metal precursor. Accordingly, there was also a disadvantage that the overall production process of the nanowire or nanomesh becomes complicated.